This invention relates generally to fluid pumps and more particularly to high-pressure-rise, low-flow-rate charging pumps for providing make-up fluids to closed high-pressure systems.
For applications such as charging pumps for supplying make-up fluid to closed high-pressure systems, it is necessary to employ pumps capable of supplying relatively low-flow-rate fluid at high pressure. It is desirable for such pumps to be highly leak resistant because of the types of fluids and the pressures involved. The most favored method of providing such leak resistance is by employment of sealless pumps. Sealless pumps often incorporate motors located inside the pump case, so there are no shaft pass-throughs to seal against leakage of the pumped fluid.
Current high-pressure-rise, low-flow-rate pumps are typically positive-displacement reciprocating pumps which are highly efficient, but, because of the necessary rotary-to-reciprocating motion converters, are large and difficult to configure as sealless pumps. Thus, when environmental considerations are important, the sealless feature becomes more important and positive-displacement reciprocating pumps become less practical due to the difficulty of adapting a reciprocating drive to a sealless pumpage-tolerant coupling mechanism. This is a serious drawback since many sealless applications rely on product lubricated bearings to reduce friction and wear in the pump equipment.
Although rotodynamic pumps are less efficient than are positive displacement pumps, they have the advantage of being much more amenable to sealless designs than are reciprocating positive displacement designs. Rotodynamic pumps are also more easily configured as sealless multi-stage machines, which permits their use in very high pressure applications. Thus, reciprocating positive displacement pumps, although more efficient than single-stage rotodynamic pumps, lose some of that efficiency advantage when multi-stage sealless features are employed.
The foregoing illustrates limitations known to exist in present low-flow-rate, high-pressure-rise pumps. Thus, it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.